1. Field of the Invention
This invention relates to a color selection mechanism for a cathode ray tube and an arm member adapted to hold thereon two frames or bars for supporting a mask of such color selection mechanism.
2. Description of the Related Art
Cathode ray tubes of various forms are conventionally known, and in a conventional color cathode ray tube of a certain form, a color selection mechanism has such a structure as shown in FIG. 4. Referring to FIG. 4, the color selection mechanism includes a pair of arm members 10, a pair of frames or support bars 12 and a mask 14. The mask 14 is a so-called aperture grill formed from a steel plate and having grid-like apertures 14A formed therein. It is to be noted that, in FIG. 4, a considerable portion of the mask 14 is omitted. The mask 14 is welded to and held taut on the frames or bars 12. The arm members 10 are joined to the frames or bars 12 by welding. Each of the conventional arm members 10 is formed from either a hollow member or a solid member and has a cross section of such an angular shape or a circular shape as shown in FIG. 5(A), 5(B) or 5(C). Each of the arm members 10 is produced by shaping such solid or hollow member into a profile of predetermined dimensions by presswork and then machining joining portions thereof, at which it is to be joined to frames or bars, so that it may have the shapes coincident with the shapes of curved surfaces of the frames or bars.
When a solid member formed by drawing is used as a material for an arm member, the arm member is heavy in weight, and it is difficult to reduce the weight of the color selection mechanism or a large size cathode ray tube. Meanwhile, a seamless pipe or a welded tube, which may be used for an arm member, is itself high in cost. Further, when a seamless pipe or a welded tube is actually used, secondary working to obtain a predetermined thickness and a predetermined sectional shape using a dice is required, and accordingly, the working cost is high. Besides, when it becomes necessary to change the size, profile and so forth of the arm member as a model change of a color cathode ray tube takes place, it is necessary to change the profile, thickness and so forth of the material itself.
When an arm member is produced from a hollow member, when the arm member 10 is welded to a frame 12, gas is produced as a result of welding, and the gas thus produced is enclosed in the hollow portion of the arm member. Consequently, there is a problem that degasification processing must be performed. Further, it sometimes occurs that washer liquid may enter the hollow portion of the arm member at a washing step after welding and post-processing for the washer liquid must necessarily be performed. Accordingly, the assembling operation of the color selection mechanism is complicated.
Furthermore, a portion of a frame at which an arm member is joined normally has a complicated curved surface. Accordingly, an arm member must be worked so that, after a solid member or a hollow member is worked by press work, the shape of a joining portion of the arm member to a frame may be Complementary to the shape of the curved surface of the frame. It is difficult to perform such working with a high degree of accuracy, and also there is a problem that the cost is increased thereby.
As described above, a conventional arm member has problems that it is high in cost and it is difficult to reduce the weight of it, that it is difficult to cope with a model change of a cathode ray tube, and that it is difficult to work and is difficult to raise the working accuracy. Also there is a problem that many steps are required for an assembling operation of a color selection mechanism.